As the feature size of the device patterns get smaller, the critical dimension (CD) requirement of features becomes a more important criterion for stable and repeatable device performance. Allowable CD variation across a substrate has also scaled with the scaling of feature CD. With lateral dimensions scaling faster than vertical dimensions, because of issues such as device capacitance, high aspect ratios (HAR) are now prevalent in the industry. When such demanding aspect ratios and CD control are compounded with requirements of high etch selectivity, sidewall smoothness and high tool throughput, the process window for any hardware configuration can become very small. In many situations, a small process window can be found only when a number of process gases are incorporated into a complex etchant gas mixture combined with extreme hardware settings, such as very high RF bias powers, to achieve a fragile balance between sidewall passivation, etch rate and mask selectivity. However, such small process windows typically suffer from performance limitations which cannot be tuned out of the etch process with known means.
Fabrication techniques often now employ a mask stack that includes a hardmask. A hardmask may be employed in the etching of high aspect ratio feature. The use of a hardmask may allow for deeper features that conventional photoresist materials cannot withstand.
Tungsten carbide (WC) films have been experimentally shown to have a high etch selectivity as a hardmask. Typically, WC films are manufactured by physical vapor deposition (PVD). These PVD films are often very rough and have a high cost of ownership (COO).
Manufacturing of plasma-enhanced chemical vapor deposition (PECVD) based WC films typically involves the use of hydrogen, a hydrocarbon source, argon, helium and a tungsten precursor. Tungsten hexafluoride (WF6) is a promising tungsten precursor due to a low cost, gaseous nature and scalability for mass production. However, the presence of fluorine in the precursor substantially lowers the adhesion to the underlayer due to the presence of fluorine based by-products like HF and CF in the process. These by-products cause the film to delaminate even under subsequent thermal stress in neutral atmospheres (e.g., 550° C. for 30 minutes in N2). Additionally, the presence of metal in the amorphous carbon leads to granular and rough surface morphology.
Therefore, there is a need in the art for cost effective methods of depositing tungsten-containing hardmask films with lower surface roughness.